DMD based flat field calibration system for MOONS

摘要

A key technical driver for the MOONS (Multi-object Optical and Near Infrared Spectrograph) instrument is to provide accurate sky subtraction using pairs of adjacent fibres. To achieve this the fibre positioners must achieve extremely close proximity, and the throughput of each fibre must be well characterised. The latter of these conditions requires a calibration system capable of creating a flat field input to the fibres to an illumination uniformity of less than 2% variation. Given the very limited space available in the instrument, a number of systems were considered to achieve this. After consideration of the available options, a novel system using a digital micromirror device (DMD) was selected for implementation. These devices has a long history in commercial displays, and provide a compact, highly responsive, and robust solution to many structured light applications. This paper explains the design and manufacture of the calibration module, as well as the intended test plan for the system.